A large earthquake swarm is occurring in the Salton Sea area just NW of Brawley, CA. The largest event so far has been a mag 5.4 tremblor which I personally felt at my home in San Diego. I am currently watching the action happen on the USGS site, and my real time Google Earth plugin. USGS reports the quakes at shallow depths of 13km (at the deepest) to <1km at the shallowest. The swarm has generated over 25 quakes at this time and is ongoing, with quakes actually getting more powerful at this time. Within one hour there were one 4.9, two 4.5 quakes, a 4.3, two quakes of 5.3 mag, plus many mag 1.0-3.9 quakes. Many smaller tremors are occurring.
*****UPDATE***** another 5.5 quake struck the same area.
The center of the activity is quite concentrated on the fault line that runs through Brawley and the Salton Sea (Salton Buttes) area. This area does have active geothermal prospecting, as well as a history of volcanic eruptions, although it has not occurred during historical time.
As these quakes are currently happening there is no data to suggest whether or not the quakes are purely tectonic, or possibly volcanic in nature. The area sees a large number of earthquakes each year, however this swarm is particularly intense for the region.
The region was shaken in 2010 by a large 7.4 magnitude earthquake centered near the Cerro Prieto volcano in Northern Mexico. The area has seen a rise in the number of very small quakes since then.
I will update this story as more info becomes available through USGS and other news media.
Below is a screen cap of the current state of the swarm, with the largest quake highlighted.
http://earthquake-report.com/2012/08/26/powerful-earthquake-swarm-in-southern-california-mexico-border/
Here is the current list of quakes in the swarm (from USGS)
*****UPDATE 8/27/12 *****
The Earthquake swarm has subsided. The majority of the quakes occurred yesterday, and slowed down to normal regional levels by late night/afternoon. Although some geologists were saying that the fault line had 'activated' and that there will probably be thousands of similar events in the coming weeks/months, I would suspect that the main events are over and we will see maybe 10-12 smaller quakes a day until even that activity subsides.
The quakes were activated by an intersection of fault lines at the base of the San Andreas fault. The area is rife with many relatively small fault lines. The last time the area was this active was in the 1970's, and before that in the 1930's. It's starting to make a pretty neat pattern of 40-year periods of quiescence, which is probably not significant in the grand scheme of things, but something worth noting nonetheless.
As it stands, the swarm had nearly 1,000 quakes, and over 400 of them were magnitude 2.5 or greater.
As I can say from firsthand experience, the shaking in San Diego was very light, almost not noticeable. The folks out there in Brawley had some minor damage to trailers, some structures, and some things were shaken off of shelves. By and large all damage was minimal, but many reports point to scared children who did not wish to go back in their houses for the night, and I am sure many residents were a bit spooked by the frequency of the quakes. one resident said they felt like they were popping off nearly every few minutes.
So far this morning, things appear to have calmed down quite considerably. The below picture shows all the quakes from yesterday's swarm.
***** UPDATE 8/28/2012 *****
After the quake swarm, scientists are weighing in on the causes. Most scientists say this is likely just a tectonic swarm, but Julie Dutton with USGS says "In volcanically active areas, earthquake swarms often indicate imminent eruptions, Dutton said. The only potential candidates for volcanic eruptions near Brawley are the Salton Buttes, five small lava domes that flank the Salton Sea and haven't erupted in close to 10,000 years." (From MSNBC.com).
While, yes, the area has not erupted in 10,000 years, it still remains geothermally active, and the area is used for geothermal energy. Chaiten volcano in Chile blew after over 10,000 years of silence, with no warning, so the possibility does always exist, however unlikely it might be. A real indicator of an imminent eruption however would be if the swarm is sustained, and the quakes grew shallower and shallower (indicating rising magma) which did not occur in this particular case.
The quakes ranged from some 13km below the surface to nearly at the surface, in a highly randomized fashion that does not seem to point to magma intrusion in the area, but like most rift-zone volcanoes, the process is highly unpredictable. More than likely the area will not see any volcanic activity for many decades to come.
*****UPDATE***** another 5.5 quake struck the same area.
The center of the activity is quite concentrated on the fault line that runs through Brawley and the Salton Sea (Salton Buttes) area. This area does have active geothermal prospecting, as well as a history of volcanic eruptions, although it has not occurred during historical time.
As these quakes are currently happening there is no data to suggest whether or not the quakes are purely tectonic, or possibly volcanic in nature. The area sees a large number of earthquakes each year, however this swarm is particularly intense for the region.
The region was shaken in 2010 by a large 7.4 magnitude earthquake centered near the Cerro Prieto volcano in Northern Mexico. The area has seen a rise in the number of very small quakes since then.
I will update this story as more info becomes available through USGS and other news media.
Below is a screen cap of the current state of the swarm, with the largest quake highlighted.
Here are some links form local news about the quakes, I will add these links as they become available.
****UPDATE****
In a statement form USGS, they stated:
“[The Brawley Seismic Zone] is a broad zone with lots of little faults,” explained Abbott.“This area has clearly activated. We will likely experience swarms of 3, 4 and 5-magnitude [earthquakes] but they are not likely to increase in intensity. Of course, there are no guarantees on this, but history says they likely won’t get bigger – that we will experience more of the same or smaller quakes,” he added.
Source: SoCal Rattled by Quake Swarms | NBC 7 San Diego
http://www.nbcsandiego.com/news/local/Brawley-Earthquake-Felt-in-San-Diego-167483415.html
http://www.sandiego6.com/news/local/Series-of-Earthquakes-Felt-in-Imperial-Valley-167480795.html
http://news.lalate.com/2012/08/26/southern-california-earthquake-today-2012-strikes-brawley-east-of-san-diego/
http://www.cbs8.com/story/19379394/53-magnitude-earthquake-shakes-near-san-diego-county
http://www.reuters.com/article/2012/08/26/us-quake-california-idUSBRE87P0C720120826
http://www.euronews.com/newswires/1636422-moderate-5-point-3-magnitude-earthquake-in-southern-california-usgs/
http://www.therepublic.com/view/story/4c38f0a1697a42f6bb9550843949e4c2/CA--SoCal-Quakes****UPDATE****
In a statement form USGS, they stated:
“[The Brawley Seismic Zone] is a broad zone with lots of little faults,” explained Abbott.“This area has clearly activated. We will likely experience swarms of 3, 4 and 5-magnitude [earthquakes] but they are not likely to increase in intensity. Of course, there are no guarantees on this, but history says they likely won’t get bigger – that we will experience more of the same or smaller quakes,” he added.
Source: SoCal Rattled by Quake Swarms | NBC 7 San Diego
http://www.nbcsandiego.com/news/local/Brawley-Earthquake-Felt-in-San-Diego-167483415.html
http://www.sandiego6.com/news/local/Series-of-Earthquakes-Felt-in-Imperial-Valley-167480795.html
http://news.lalate.com/2012/08/26/southern-california-earthquake-today-2012-strikes-brawley-east-of-san-diego/
http://www.cbs8.com/story/19379394/53-magnitude-earthquake-shakes-near-san-diego-county
http://www.reuters.com/article/2012/08/26/us-quake-california-idUSBRE87P0C720120826
http://www.euronews.com/newswires/1636422-moderate-5-point-3-magnitude-earthquake-in-southern-california-usgs/
http://earthquake-report.com/2012/08/26/powerful-earthquake-swarm-in-southern-california-mexico-border/
Here is the current list of quakes in the swarm (from USGS)
*****UPDATE 8/27/12 *****
The Earthquake swarm has subsided. The majority of the quakes occurred yesterday, and slowed down to normal regional levels by late night/afternoon. Although some geologists were saying that the fault line had 'activated' and that there will probably be thousands of similar events in the coming weeks/months, I would suspect that the main events are over and we will see maybe 10-12 smaller quakes a day until even that activity subsides.
The quakes were activated by an intersection of fault lines at the base of the San Andreas fault. The area is rife with many relatively small fault lines. The last time the area was this active was in the 1970's, and before that in the 1930's. It's starting to make a pretty neat pattern of 40-year periods of quiescence, which is probably not significant in the grand scheme of things, but something worth noting nonetheless.
As it stands, the swarm had nearly 1,000 quakes, and over 400 of them were magnitude 2.5 or greater.
As I can say from firsthand experience, the shaking in San Diego was very light, almost not noticeable. The folks out there in Brawley had some minor damage to trailers, some structures, and some things were shaken off of shelves. By and large all damage was minimal, but many reports point to scared children who did not wish to go back in their houses for the night, and I am sure many residents were a bit spooked by the frequency of the quakes. one resident said they felt like they were popping off nearly every few minutes.
So far this morning, things appear to have calmed down quite considerably. The below picture shows all the quakes from yesterday's swarm.
***** UPDATE 8/28/2012 *****
After the quake swarm, scientists are weighing in on the causes. Most scientists say this is likely just a tectonic swarm, but Julie Dutton with USGS says "In volcanically active areas, earthquake swarms often indicate imminent eruptions, Dutton said. The only potential candidates for volcanic eruptions near Brawley are the Salton Buttes, five small lava domes that flank the Salton Sea and haven't erupted in close to 10,000 years." (From MSNBC.com).
While, yes, the area has not erupted in 10,000 years, it still remains geothermally active, and the area is used for geothermal energy. Chaiten volcano in Chile blew after over 10,000 years of silence, with no warning, so the possibility does always exist, however unlikely it might be. A real indicator of an imminent eruption however would be if the swarm is sustained, and the quakes grew shallower and shallower (indicating rising magma) which did not occur in this particular case.
The quakes ranged from some 13km below the surface to nearly at the surface, in a highly randomized fashion that does not seem to point to magma intrusion in the area, but like most rift-zone volcanoes, the process is highly unpredictable. More than likely the area will not see any volcanic activity for many decades to come.
